Method and means for making dental impressions

ABSTRACT

A method of impression making for use in dentistry wherein a clear plastic impression tray is stabilized in position in the mouth without any impingement of hard or soft tissue, the impression tray being stabilized and held in the mouth by the patient while the impression material is injected into the stabilized tray by a special injector gun, in such a manner as to produce an impression with neither displacement of the soft tissue, nor entrapment of any air or saliva.

United States Patent 1 Colman et a1.

[ METHOD AND MEANS FOR MAKING DENTAL IMPRESSIONS [76] Inventors: AlbertJ. Colman, 427 North Carnden Drive, Beverly Hills, Calif.; Paul I.Zandberg, 8202 Romaine Street, Los Angeles, Calif. 90046; Charles F.Taylor, 150 East Industry, LaHabra, Calif. 90631 [22] Filed: Dec. 4,1970 [21] Appl. No.2 95,100

[52] US. Cl. ..32/17 [51] Int. Cl ..A6lc 9/00 [58] Field of Search..32/17; 222/413, 326, 327

[56] References Cited UNITED STATES PATENTS 4/1962 Zandberg ..32/6O4/1939 Sitkinetal.....

[451 Mar. 27, 1973 2,452,903 11/1948 Cofiey ..32/17 OTHER PUBLlCATIONSDental Survey, New Technique by John Bunyan, March 1936, page 62.

Primary Examiner-Robert Peshock Attorney-J. Calvin Brown ABSTRACT Amethod of impression making for use in dentistry wherein a clear plasticimpression tray is stabilized in position in the mouth without anyimpingement of hard or soft tissue, the impression tray being stabilizedand held in the mouth by the patient while the impression material isinjected into the stabilized tray by a special injector gun, in such amanner as to produce an impression with neither displacement of the softtissue, nor entrapment of any air or saliva.

17 Claims, 18 Drawing Figures PATENTEDMARZYISYS FlG./.

SHEET 10F 2 SHEET-l IIHI [I I] ll lllllll III INVENTOR5 PAUL Z ANDBER 6ALBERT J. COLMAN BY CHARLES E 'L'AYLOR 147' TORNE Y PATH-HEUMARZYIUH3,722,097,

SHEET 2 BF 2 2- SHEE rssnszr-2 9/ H a. i7

INVENTORS PAUL I. ZANDBERG ALBERTJ. COLMAN BY CHARLEs F, TAYL ORATTORNEY METHOD AND MEANS FOR G DENTAL IMPRESSIONS BACKGROUND OF THEINVENTION 1. Field of the Invention This invention has application tothe entire scope of impression making in dentistry. Any time that anaccurate cast replica of hard or soft tissues of the mouth is desired,this invention is applicable. The areas involved are those of thescience of the materials as well as the scope or field of application ofthe technique.

2. Description of the Prior Art H The art of impression making as itexists today in dentistry can be described as a procedure that utilizesa device (tray) to carry to the mouth some type of material that haseither a chemical or thermal set. The tray is filled with the material,introduced into the mouth, and the desired imprint obtained. There arecertain short-comings or difficulties in the usual impression proceduresthat necessitate many involved steps to try to help prevent theshort-comings or errors from occuring. For example: if the desire is toobtain an accurate imprint or impression of the existing teeth toaccurately determine the state of the occlusion of examining it outsideof the mouth, it becomes necessary to use some method of registering thedepths of the crevices of the teeth without trapping air or saliva;otherwise a void will occur in the impression, with a corresponding plusarea in the poured study cast.

The two most frequently used techniques for eliminating these defectareas are to either finger wipe the impression material onto thesurfaces of the teeth before inserting the filled tray and/or removingthe plus areas with a sharp instrument from the hardened poured cast. Apreferred, but less used method, is to use a small syringe that has anarrow opening, approximately 1% 1 mm., and inject the impressionmaterial slowly around the teeth and then seat the larger tray filledwith a bulk of impression material. The first two techniques are fraughtwith error and the third is laborious and difficult.

Many other impression procedures frequently used in dentistry todayinvolve a two-visit or two-step procedure. A preliminary impression isobtained first, a cast poured, a custom tray fabricated on the originalcast, the custom tray refined in the mouth, and then a final impressionobtained in the custom tray. A problem of the custom tray typeimpression is that it frequently renders an impression that can lookperfect but because of the great pressures that may be produced withinits closely adapted fit, it can frequently cause distortion of softtissues when the final impression is registered.

Other attempts have been made to overcome some of these impressionproblems. Seeger in 1890, U.S. Pat. No. 432,909; Wentzel in 1951, U.S.Pat. No. 2,594,832; Wagner in 1954, U.S. Pat. No. 2,722,744; Brant in1957, U.S. Pat. No. 2,860,414, and Zandberg in 1961, developedadjustable trays that would more accurately conform to the anatomy ofthe mouth, thus hoping to eliminate the necessity of a preliminaryimpression followed by the construction of a custom impression tray forregistering the final impression. None of these attempts became popular,as they fell short of their goal.

The technique of Coffey in U.S. Pat. No. 2,458,l45 which was issued in1949, attempted to reduce or eliminate some other impression problems.By injection molding the impression material he hoped to eliminatedistortion of the gums. The theory was correct, the devices described,made it fall short of this goal. The shape of the impression trays andthe site of attachment of the nipple or injector tube on Coffeys tray,distorted the oral structures. There was no way of being certain thatthe under surface of the tray, when placed in the mouth was notimpinging upon nor displacing soft tissues. Lastly, there was no way ofcontrolling the injecting pressure in Coffeys injecting gun, making itpossible to cause not only displacement of soft tissues, but movement ofthe tray.

SUMMARY This is a system of impression making for dentistry that, foredentulous mouths combines the advantages of mucostatics with theadvantages of fully border molded impressions by recording bothperipheral height and thickness as well as an undistorted registrationof the bearing area. The same principles apply to dentulous mouths withthe added advantages of having a controlled amount of impressionmaterial surrounding all teeth; thus eliminating distortion from toothin areas. Both types of impressions yield virtually bubble freereproductions of all tooth and soft tissue anatomic detail.

In order to achieve these results, an empty clear plastic impressiontray is stabilized in position and any impingement of hard or softtissue visualized and eliminated. The impression material is theninjected into the stabilized tray by using a special injector gun. Thistechnique and armamentarium gives a superior final impression withoutthe necessity of a preliminary impression and a special custom tray.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation, partly infragment of a tray of the invention within a patients mouth and a gunfor injecting impression material within the tray;

FIG. 2 is a fragmentary, sectional view on an enlarged scale of the gunshown in FIG. 1;

FIG. 3 is a fragmentary sectional view, on an enlarged scale, taken onthe line 3-3 of FIG. 2;

FIG. 4 is a fragmentary, sectional view, on an enlarged scale, taken onthe line 4-4 of FIG. 2;

FIG. 5 is a fragmentary enlarged view of mechanism used in moving thepiston of the gun shown in FIG. 2;

FIG. 6 is a top plan view of a maxillary tray used in the practice ofthe invention;

FIG. 7 is a sectional view of the line 7-7 of FIG. 6;

FIG. 8 is a posterior end elevation of the tray shown in FIG. 6;

FIG. 9 is a top plan view of a mandibular tray;

FIG. 10 is a cross sectional view on the line 10-10 of FIG. 9;

FIG. 11 is a posterior end view of the tray of FIG. 9;

FIG. 12 is a top plan view of a maxillary tray;

FIG. 13 is a sectional view on the line 13-13 of FIG. 12;

FIG. 14 is a posterior end view of the tray shown in FIG. 12;

FIG. 15 is a top plan view of a mandibular tray;-

DESCRIPTION OF THE PREFERRED EMBODIMENT The gun for injecting impressionmaterial within a tray will be described first.

The gun 1 shown as an entirety in FIGS. 1 and 2, in-

cludes a hand grip, stock, or handle 2 communicating with a casing orhousing 3 and a rear casing extension 4 joining with the casing orhousing 3. In the present instance the stock, housing or casing islongitudinally split, as shown in FIGS. 3 and 4 to provide twocooperating parts joined together, as shown at 5 and 6. A tubularextension 7 is secured to the housing or casing 3 and this extensionreceives one end of a tubular barrel or cylinder 8. A plunger or piston9 is provided with a stem 10 receivable within the extension 4 thus thepiston and stem is capable of movement throughout the length of thebarrel or cylinder 8 when the stem which is provided with a rack 11 isactuated by a train of gears within the housing or casing 3. The outerend of the cylinder 8 is provided with a conical head 12. The barrel orcylinder 8 is adapted to receive impression material which is to beejected through the conical head when the piston 9 is moved in onedirection. To move the piston and the stem, we provide within thehousing or casing 3 suitable gears mounted on axles. Thus referring toFIG. 3, a ratchet 20 meshes with a gear 21 mounted on shaft 22 whichalso mounts a gear 23. Gear 23 meshes with gear 24 mounted on shaft 25.Gears 27 and 28 are mounted on shaft 29, gear 27 being in mesh with gear24 while gear 28 meshes with the teeth of the rack 11. With reference toFIG. 3, it will be noted that the rack type stem passes between thespaced gears 21 and 23. The ratched wheel 20 is moved by a trigger asshown best in FIG. 5 wherein the trigger 30 is pivoted at 31 within thehousing or casing and the trigger is provided with a hook type pawl 32,the hook end of which engages a tooth of the ratchet wheel 20. A secondhook type pawl 33 diametrically engages a tooth of the ratchet wheel 20and the trigger and the pawl arm 33 are connected by means of a link 34,the link being pivoted at 35 to the trigger and extends between twoguide members 36 and 37, the pawl 33 extending freely through an end ofthe link. Paw] arm 33 is supported within the handle or stock in themanner shown in FIGS. 2 and 3 at 38 which comprises two spaced apartlugs 39 and 40, the end of the pawl armbeing bent at 41 for receptionbetween said lugs, there also being a lug at 42 bearing against the pawlarm so as to maintain the portion 41 between the lugs 39 and 40. Whenthe trigger is moved inwardly toward the stock or handle, pawl 32 turnsthe ratchet wheel a slight amount while the pawl arm 33 is moved fromengagement with the teeth of the ratchet wheel by the link 34. In thismanner the piston is moved within the barrel progressively, that is tosay, it is first moved and then as the trigger is released, there is apause in the movement of the piston whereupon the piston is again movedwhen the trigger is moved. This provides what may be designated asinterrupted movement and after the piston has made an excursion withinthe cylinder, it may be moved from the outer end of the cylinderinwardly to the position shown in FIG. 2 by movement of the triggertoward the stock which releases both pawls from engagement with theratchet wheel 20. the piston is then returned to the position of FIG. 2manually. If there is back pressure exerted against the piston greaterthan 1% PSI, movement of the trigger will not move the piston but thetrigger in its movement will cause the pawls 32 and 33 to release theirengagement with the ratchet wheel so that the piston remains stationary.

The trays for which the gun is employed are shown in FIGS. 6 to 18inclusive and a specimen tray is shown at 50 positioned within the mouthof a patient. This tray, like all of the trays shown in the remainingFigures, is provided with an external tube communicating with thechannel portion of the tray and with a tube 51, which tube connects withthe outlet end 52 of the conical head for the cylinder or barrel. Thebarrel 8 holds impression material which is progressively orinterruptedly fed from the barrel into the tray as the trigger is movedin one direction followed by relaxation or stoppage of movement as thetrigger assumes its forward position, as shown in FIGS. 1 and 2. Torecapitulate, the manually driven ratchet wheel 20 meshes with anddrives gear 21. Gear 21 is on the same shaft 22 with gear 23 and gear 23in turn drives gear 24 mounted on shaft 25. As shown in FIG. 5, gear 24drives gear 27 which is mounted on the same shaft 29 as gear 28 and gear28 in turn meshes with the teeth of the rack. The gear ratio is suchthat the plunger moves forwardly approximately 1/16 inch in the barrelwith each reciprocation of the trigger.

Reference is now made to sheet 2 and FIGS. 6 to 18 inclusive, whichillustrate the tray construction. All of the trays are formed from acrystal clear material and which may be formed from an acrylic resin orfrom a styrene. FIGS. 6 and 8 inclusive are maxillary and FIGS. 9 to 11mandibular trays for edentulous jaws. While the trays shown in FIGS. 12to 18 are maxillary and mandibular for dentulous mouths. The maxillaryedentulous tray shown in FIGS. 6, 7 and 8, is designated as 60, thelabial flange 61 inclines toward the lingual so as to fit the anteriorresidual ridge. The flange thusly conforms to the labial vestibulerather than distorting the lip. The tray has large areas 62 over theridge crest to allow for a non-pressure flow of impression material. Theinjector tube 63 is attached to the tray over the crest of the anteriorresidual ridge and is angled in such a way that it does not interferewith the normal relaxed position of the upper lip thus allowing theinjector tube 63 to exit from the mouth between the upper and lower lipswith no displacement of either lip. The angle of the injector tube 63 issuch that when the tray is positioned correctly in the mouth of thepatient, the tube is substantially horizontal, as shown at 64 in FIG. 7.As previously pointed out, the injector tube is adapted to be connectedto the conical head outlet 52 of the injector gun.

The edentulous mandibular tray shown in FIGS. 9 to 11 inclusive isdesignated as and as in the case of the tray 60 has an anatomic shapeand is provided with a flanges is an occlusal wall 74. The injector tube75 is similar in detail to injector tube 63 in that it has substantiallya horizontal portion 76 and an angular portion 77 leading to theinterior of the tray. It will be observed that the flanges are ofrelatively long length in the posterior lingual area.

The dentulous maxillary tray of FiGS. 12, 13 and 14, is designated as80. It will be noted that the inclined labial flange 81 of tray 80closely follows the normal inclined angle of natural anterior teeth toprevent the incisal edges of the anterior teeth from striking the labialwall of the tray. This tray is formed to have a widened space 82 for thetooth-row provided by the narrower palatal portion 83 of the tray. Theinjector tube 84 is attached over the anterior teeth section of the traywhereby it does not interfere with the normal relaxed position of theupper lip, thus allowingit to exit from the mouth between the upper andlower lips with no displacement of either lip. This tray, like tray 60,provides platforms 85 for the addition of external stabilizing wax ashereinafter described in the statement of operation.

The mandibular dentulous tray shown in FIGS. 15, 16, 17 and 18 isdesignated as 90. This tray follows generally the construction of tray80 in the provision of an inclined labial flange 91 and the method ofattachment of the injector tube 92 to the tray. Tray 90 provides a widerbuccal-lingual dimension and long length flanges in the posteriorlingual area. As shown in FIG. 18 the lingual flange is of greater depththan the buccal flange. Platforms 100 are provided for the addition ofexternal stabilizing wax as hereinafter set forth.

The impression material is characterized in that it has low viscosityand may be a modified alginate, a polysulfide, a silicone rubber or anagar hydrochloride, to name a few. As stated, it should be of lowviscosity and the impression material is placed within the gun cylinderor barrel with the piston retracted as shown in FIG. 2. After the trayhas been correctly positioned within the mouth of the patient ashereinafter set forth in discussion of the maxillary impression andmandibular impression for both dentulous and edentulous mouths, thetrigger of the gun is actuated to cause the piston to move theimpression material from the gun into the tray. The gun is designed sothat if a back pressure in excess of 1% PSI is encountered in injectingthe impression material from the gun into the tray, the piston will notadvance due to slippage of the pawls in the contact with the ratchetwheel 20. There will also be a slippage of the pawls so that the pistondoes not advance if the trigger of the gun is operated too rapidly toprovide a rapid injection of the impression material or if too viscousimpression material is used. Thus minimum pressure and interruptedadvancement of the piston prevents any pressure from being transmittedto the soft tissues in the mouth and thus an impression can be recordedwithout displacing any soft tissues. The clear plastic trays enable thedentist to correctly position the trays within the mouth prior to thegun injecting the impression material into the tray. All of the traysdescribed provide ample tissue room for the flow of impression materialas well as conforming closely to the anatomic details of the mouth.Furthermore, the interrupted movement of the piston of the gun iseffective in removing air from the impression material and results in anaccurate impression which is free from the defects which frequentlyoccur in most impressions.

The technique of operation is as follows:

First a correct size anatomic injector tray is selected for the patientsmandible or maxilla. The Maxillary Impression:

The maxillary tray is stabilized in position by placing a pea sizedmound of stabilizing wax over the stop nub 64a on the tray in the rugaearea. A strip of stabilizing wax is also placed along the distal borderof the tray just distal to the vibrating line of the soft palate. Avisual check is made intra-orally and any areas of impingement arechecked for and eliminated. Palatal impingement is eliminated by eitheradding a larger amount of stabilizing wax in the rugae area or byselecting a different size tray. Peripheral flange placement should bewithin three-sixteenths of an inch of the depth of the vestibular fold.This distance must not be observed by pulling the cheeks laterally, butchecked without displacing the cheeks. Impingement or overextension inthe peripheral areas is corrected by grinding away the plastic tray.Under-extended areas are modified by the addition of small amounts ofstabilizing wax, being certain not to over-extend with the wax.

Enough stabilizing wax is next added to the external surface of the traythat will allow the patient to close into it and stabilize the tray inposition in the mouth. This wax is added in the posterior area where thestabilizing wax platforms 65 are located, as the occlusal pressure ofthe patient must be confined to the posterior strip of wax across thevibrating line, that will then be the only area of soft tissue distortedfrom rest, when the impression is recorded. The tray is inserted andremoved several times, this familiarizes the operator with the traysexact placement and stabilization position; thus insuring a finalplacement that is free from impingement when the impression is actuallyrecorded. The tray is removed from the mouth and air dried. An alginateimpression adhesive is applied to the inside and peripheral edges of thetray. A special alginate impression material (roughly half again as muchwater) is mixed and inserted into the injector gun. Any elasticimpression material that will have sufficient body to not run out of thetray, once it is filled in the mouth and yet of a viscosity that is lowenough so that any back pressure created in the gun can be kept below 1%pounds PS1, will work in this procedure. The tray is again stabilized inthe mouth. The injection rate must be fast enough to get the materialinto the mouth before gelation begins, but slowly enough to enable theoperator to visualize (at the transparent injector tube attached to thetray) a relaxation of impression material flow between each advancementof the piston of the injector gun. The ratchet mechanism of the injectorgun, if advanced slowly enough, will cause this very necessaryinterrupted flow of impression material into the mouth. As mentionedabove, this interrupted injection rate can be observed through the clearplastic injector tube of the tray. Three minutes after initial set, theimpression is removed from the mouth and poured immediately with anaccelerated mix of dental stone. The Mandibular impression:

The technique is carried out as described above except that stabilizingwax is placed on both buccal shelf areas only. The external stabilizingwax for the opposing occlusal stabilization is placed over the sameareas where the underlying stabilizing wax has been placed, at the sitesof the stabilizing wax platforms.

We claim:

1. Means for making dental impressions including an impression trayadapted for insertion into the mouth of the patient, a low viscosityimpression material for application to said impression tray, a gun forholding said impression material detachabley engaged with saidimpression tray, said gun including means for feeding said impressionmaterial into said impression tray, and pressure-responsive meanscarried by said gun in operative engagement with said means for feedingsaid impression material from said gun to said tray for preventing theflow of impression material into said impression tray upon build-up of apredetermined back pressure against said means for feeding theimpression material into the impression tray.

2. The means of claim 1, wherein said impression tray includes a channelportion and a tube at the front of the tray in communication with saidchannel portion, and said tube includes two portions angularly disposedwith respect to each other, one of said portions being angularlyconnected to said tray, and the other angular portion being engaged bysaid means for injecting the impression material into the tray, theangular relationships of the angular portions with respect to each otherand to the tray being such that when the tray is in position in themonth, said other angular portion extends from the mouth in asubstantially horizontal plane.

3. The means of claim 1 with the addition of means for intra-orallyvisualizing a space between said tray and the mouth structure toaccurately position the tray and avoid impingement of hard or soft mouthtissue.

4. The means of claim 3 wherein said means for intra-orally visualizingthe space between the tray and the mouth structure comprises theconstruction of the tray with a clear translucent material.

5. The means of claim 1 with the addition of wax-like stabilizing meansattached to said tray for accurately positioning and maintaining thetray in the mouth.

6. The means of claim 1, wherein the front of the im pression tray is atan acute angle with the floor of the tray to give the tray the samecontour as the space between the lip and the jaw and not to touch ordistort the soft tissue covering the jaw or lip, nor to touch the frontteeth.

7. The means of claim 1 wherein the peripheral edge of the tray iscontoured to follow the shape of the human mouth without touching thesoft tissue.

8. The means of claim 1, wherein said tray has a labial flange thatforms an acute angle with the occlusal surface of the tray.

9. The means of claim 1, with the addition of nubs and platforms on saidtray, and stabilizing wax attached to said nubs and platforms foraccurately positioning and maintaining the tray in the mouth.

10. The means of claim 1, wherein said gun includes a housing, a handgrip connected to said housing, a cylindrical member for holding saidimpression material, one end of said cylindrical member being connectedto said housing and the opposite end thereof being provided with anoutlet opening for communication with the tube of said impression tray,a piston movable through said cylindrical member for moving the impression material towards the outlet opening, a trigger operativelymounted in said hand grip, and actuating means connecting said triggerand piston for advancing the latter in said cylindrical member inresponse to the operation of the former.

11. The means of claim 10, wherein said actuating means include a rackconnected to, and movable with, said piston, a train of gearsoperatively engaged with said rack, and pawl means operatively engagedwith said gear train and trigger for actuating the former upon operationof the latter.

12. The means of claim 11, wherein said pawl means slips upon exertionof a predetermined back pressure on said impression material to preventthe forcing of impression material into said tray under increasedpressure of a sufficient degree to cause tissue displacement.

13. Means for making dental impressions including an impression tray,said tray having a channel portion and a trube at the front of the trayin communication with said channel portion, said tray being constructedof a clear, translucent material for intra-orally visualizing a spacebetween said tray and the mouth structure to accurately position thetray and avoid impingement of hard or soft mouth tissue, wax-likestabilizing means positioned on said tray for maintaining the tray inposition in the mouth, a low viscosity impression material forapplication to said impression tray, a gun for holding said impressionmaterial detachably engaged with said impression material into saidimpression tray, and pressure-responsive means carried by said gun inoperative engagement with said means for feeding said impressionmaterial from said gun to said tray for preventing the flow ofimpression material into said impression tray upon build-up of apredetermined back pressure against said means for feeding theimpression material into the impression tray.

14. The means of claim 13 wherein said gun includes a housing, a handgrip connected to said housing, a cylindrical member for holding saidimpression material, on end of said cylindrical member being connectedto said housing and the opposite end thereof being provided with anoutlet opening for communication with the tube of said impression tray,a piston movable through said cylindrical member for moving theimpression material towards the outlet opening, a trigger operativelymounted in said hand grip, and actuating means connecting said triggerand piston for advancing the latter in said cylindrical member inresponse to the operation of the former.

15. The means of claim 14, wherein said actuating means include a rackconnected to, and movable with, said piston, a train of gearsoperatively engaged with said rack, and pawl means operatively engagedwith said gear train and trigger for actuating the former upon operationof the latter.

16. The means of claim 15, wherein said pawl means slips upon exertionof a predetermined back pressure on said impression material to preventthe forcing of impression material into said tray under increasedpressure of a sufficient degree to cause tissue displacement.

17. The means of claim 15 wherein said pawl means slips if there is backpressure created against said piston in excess of 1% psi.

1. Means for making dental impressions including an impression trayadapted for insertion into the mouth of the patient, a low viscosityimpression material for application to said impression tray, a gun forholding said impression material detachabley engaged with saidimpression tray, said gun including means for feeding said impressionmaterial into said impression tray, and pressure-responsive meanscarried by said gun in operative engagement with said means for feedingsaid impression material from said gun to said tray for preventing theflow of impression material into said impression tray upon build-up of apredetermined back pressure against said means for feeding theimpression material into the impression tray.
 2. The means of claim 1,wherein said impression tray includes a channel portion and a tube atthe front of the tray in communication with said channel portion, andsaid tube includes two portions angularly disposed with respect to eachother, one of said portions being angularly connected to said tray, andthe other angular portion being engaged by said means for injecting theimpression material into the tray, the angular relationships of theangular portions with respect to each other and to the tray being suchthat when the tray is in position in the mouth, said other angularportion extends from the mouth in a substantially horizontal plane. 3.The means of claim 1 with the addition of means for intra-orallyvisualizing a space between said tray and the mouth structure toaccurately position the tray and avoid impingement of hard or soft mouthtissue.
 4. The means of claim 3 wherein said means for intra-orallyvisualizing the space between the tray and the mouth structure comprisesthe construction of the tray with a clear translucent material.
 5. Themeans of claim 1 with the addition of wax-like stabilizing meansattached to said tray for accurately positioning and maintaining thetray in the mouth.
 6. The means of claim 1, wherein the front of theimpression tray is at an acute angle with the floor of the tray to givethe tray the same contour as the space between the lip and the jaw andnot to touch or distort the soft tissue covering the jaw or lip, nor totouch the front teeth.
 7. The means of claim 1 wherein the peripheraledge of the tray is contoured to follow the shape of the human mouthwithout touching the soft tissue.
 8. The means of claim 1, wherein saidtray has a labiaL flange that forms an acute angle with the occlusalsurface of the tray.
 9. The means of claim 1, with the addition of nubsand platforms on said tray, and stabilizing wax attached to said nubsand platforms for accurately positioning and maintaining the tray in themouth.
 10. The means of claim 1, wherein said gun includes a housing, ahand grip connected to said housing, a cylindrical member for holdingsaid impression material, one end of said cylindrical member beingconnected to said housing and the opposite end thereof being providedwith an outlet opening for communication with the tube of saidimpression tray, a piston movable through said cylindrical member formoving the impression material towards the outlet opening, a triggeroperatively mounted in said hand grip, and actuating means connectingsaid trigger and piston for advancing the latter in said cylindricalmember in response to the operation of the former.
 11. The means ofclaim 10, wherein said actuating means include a rack connected to, andmovable with, said piston, a train of gears operatively engaged withsaid rack, and pawl means operatively engaged with said gear train andtrigger for actuating the former upon operation of the latter.
 12. Themeans of claim 11, wherein said pawl means slips upon exertion of apredetermined back pressure on said impression material to prevent theforcing of impression material into said tray under increased pressureof a sufficient degree to cause tissue displacement.
 13. Means formaking dental impressions including an impression tray, said tray havinga channel portion and a trube at the front of the tray in communicationwith said channel portion, said tray being constructed of a clear,translucent material for intra-orally visualizing a space between saidtray and the mouth structure to accurately position the tray and avoidimpingement of hard or soft mouth tissue, wax-like stabilizing meanspositioned on said tray for maintaining the tray in position in themouth, a low viscosity impression material for application to saidimpression tray, a gun for holding said impression material detachablyengaged with said impression material into said impression tray, andpressure-responsive means carried by said gun in operative engagementwith said means for feeding said impression material from said gun tosaid tray for preventing the flow of impression material into saidimpression tray upon build-up of a predetermined back pressure againstsaid means for feeding the impression material into the impression tray.14. The means of claim 13 wherein said gun includes a housing, a handgrip connected to said housing, a cylindrical member for holding saidimpression material, on end of said cylindrical member being connectedto said housing and the opposite end thereof being provided with anoutlet opening for communication with the tube of said impression tray,a piston movable through said cylindrical member for moving theimpression material towards the outlet opening, a trigger operativelymounted in said hand grip, and actuating means connecting said triggerand piston for advancing the latter in said cylindrical member inresponse to the operation of the former.
 15. The means of claim 14,wherein said actuating means include a rack connected to, and movablewith, said piston, a train of gears operatively engaged with said rack,and pawl means operatively engaged with said gear train and trigger foractuating the former upon operation of the latter.
 16. The means ofclaim 15, wherein said pawl means slips upon exertion of a predeterminedback pressure on said impression material to prevent the forcing ofimpression material into said tray under increased pressure of asufficient degree to cause tissue displacement.
 17. The means of claim15 wherein said pawl means slips if there is back pressure createdagainst said piston in excess of 1 1/2 psi.